1. Field of the Invention
The invention relates to a UHF phase shifter and its application to an array antenna. The invention relates more particularly to a liquid-crystal phase shifter for UHF signals.
Such a phase shifter is suitable for controlling signals the frequency of which may typically stretch from 1 to 100 GHz. It essentially includes a UHF waveguide filled with an electrooptical material the permittivity of which is controlled particularly by electrical means.
2. Discussion of Background
The majority of electronic scanning antennae, except for antennae with active modules, use ferrite-type or diode-type phase shifters (such as the antennae of "RADANT" type) controlled magnetically. By virtue particularly of their low insertion losses, ferrite-type shifters have the advantage of withstanding high powers. However, they exhibit the drawbacks of being heavy, bulky and relatively sensitive to variations in temperature.
PIN-diode type phase shifters are used mainly in active antennae. They exhibit the advantages of being light, compact and fairly insensitive to temperature variations as well as the drawbacks of higher insertion losses and thus less good resistance to high powers.
Diode-type phase shifters are essentially of two types.
switching type. They cause the signal to flow over different path lengths and are suitable for high phase shifts (.pi./2 or .pi.).
perturbation type. They bring variable impedances onto the transmission line and are rather intended for low phase shifts (.pi./8 or .pi./4).